1. Field of the Invention
The present invention relates to a film thickness measuring method, a relative dielectric constant measuring method, a film thickness measuring apparatus, and a relative dielectric constant measuring apparatus in each of which an insulator film formed on a surface of a semiconductor substrate is an object to be measured.
2. Description of Related Art
A semiconductor device is to be produced by forming, on a semiconductor substrate, a variety of films including an insulator film. The characteristics of the insulator film have a great influence on the characteristics of the semiconductor device. It is therefore inevitable to evaluate the characteristics of the insulator film during the semiconductor device production processing.
With the progress of semiconductor device integration technology, the type and thickness of an insulator film have undergone a change. This has consequently changed the insulator film evaluation method. For example, there have been instances where an optical method (e.g., ellipsometry) is used as a method of measuring the thickness of an insulator film. Such an optical method could not always achieve an accurate measurement under the influence of an organic substance attached to the insulator film surface. Therefore, attention is now placed on an electric film thickness measuring method directly related to the device operation.
With the progress of the multilayer-film technology of forming wirings as sandwiching an interlayer insulator film, the relative dielectric constant of the insulator film becomes an important parameter. It is therefore required to measure more accurately the relative dielectric constant of the insulator film.
In the insulator film, the film thickness can be obtained when the surface charge amount, the surface potential and the relative dielectric constant are known. The relative dielectric constant can be obtained when the surface charge amount, the surface potential and the film thickness are known. Accordingly, when either the film thickness or the relative dielectric constant is known in addition to the surface charge amount and the surface potential, the other can be obtained.
In measurement of the film thickness or relative dielectric constant of an insulator film, there is a measuring method in which electrodes are formed on the surface of the insulator film. However, this method is not desirable because this is a destructive test and includes a number of processing steps. There is also a measuring method using mercury as electrodes. However, the mercury is detrimental to the human body and is therefore hard to deal with. Further, when the electrodes are formed on the surface of the insulator film, this involves the likelihood that an electric current leaks through the insulator film at the time of measurement, making the measurement inaccurate.
It is therefore desired to establish a method of measuring, in a non-contact manner, the thickness or relative dielectric constant of an insulator film. Examples of such a method include a method of measuring the surface charge amount and surface potential of an insulator film at the time when the insulator film surface is electrically charged by corona discharge, and of obtaining, based on the values thus measured, the thickness or relative dielectric constant of the insulator film.
However, the surface charge amount of the insulator film could not conventionally been measured directly. As a matter of fact, the charge given to the insulator film at the time of corona discharge has been measured by a Coulomb meter, or the electric current flowing to the semiconductor substrate has been measured. Based on the values thus measured, the insulator film surface charge amount has been obtained indirectly.
With the progress of the semiconductor technology, the pattern is increasingly miniaturized. Accordingly, the gate oxide layer becomes thinner and the interlayer insulator film is lowered in dielectric constant. Further, there exists an electric current which leaks through the insulator film. Accordingly, the insulator film surface charge amount could not accurately be obtained by the indirect measuring method above-mentioned. Thus, the thickness or relative dielectric constant of an insulator film could not be accurately measured.